An ironless linear motor is preferable for machining tools and semiconductor manufacturing devices which need precise positioning since it has no cogging caused by an iron core. Japanese Patent Laid-Open No. 10-23735 discloses an ironless AC multi-phase linear motor having cooling tubes for cooling ironless coils. A carrier of this linear motor includes permanent magnets which are provided on a magnet plate so as to form a magnetic gap, and a stator includes U-phase, V-phase and W-phase ironless coils arranged in a row in the movement direction. Two copper round pipes as cooling tubes pass through holes of the ironless coils. The two round pipes are remote from each other sandwiching the magnetic gap such that a magnetic flux generated by permanent magnets does not penetrate the two round pipes. Therefore, eddy current, which is generated when an electrically conductive body crosses the magnetic field, is prevented and viscous resistance is not generated.
Japanese patent Laid-Open No. 10-23735 further discloses a single, flat, cooling tube keeping in touch with all inner surfaces of ironless coils. This flat cooling tube has a higher cooling efficiency than the two round pipes. The Japanese Patent Laid-Open No. 10-23735 further discloses a single flat multi-bore cooling tube formed by adhering eight cooling pipes insulated from each other. The flat multi-bore cooling tube increases cooling efficiency and decreases eddy current.
The above-noted technology and other related technology does not have a high cooling efficiency which can reduce cogging and keep a constant thrust in a simple way and does not have a high cooling efficiency which can reduce viscous resistance.